I didn't want to tell anyone until I had verified the exact measurements. But it is either a 622mm at about f2.7 or it is 405mm at f1.5. I'm working on some answers for that and will be sure to update.

Not sure what the lens structure is and no - don't grind my own. It is from a larger optical assembly.
Incidentally my camera can focus it from about 16" behind the rear flange. Which means the barrel will be quite short.